The present invention relates to adhesive emulsion compositions for use on polyolefin substrates to promote adhesion thereto wherein the compositions have improved environmental properties, and specifically no substantial organic emissions.
As is well known to those skilled in the art, polyolefins are widely used in the plastics industry in the molding of a variety of products. Ever increasing among such products are molded parts for automobiles because of the resistance of such polyolefins to corrosion. One of the difficulties that has long existed in the use of polyolefins in the production of molded plastic parts is the inability to establish a secure bonding relationship between the polyolefin and any coatings to be applied to it, notably including paint coatings.
It has been proposed to employ, as an adhesion-promoting primer for polyolefins, and notably polypropylenes, a primer composition which is formulated to contain a chlorinated polyolefin. Eastman Chemical Products, Inc. has made and sold, for some time, such chlorinated polyolefins for use as adhesion promoters to polyolefins generally. Eastman, in its product brochure entitled "Eastman Chlorinated Polyolefins in Coatings for Selected Plastics" (Aug. 1988), suggests that a composition be formulated to include a chlorinated polyolefin solution sold under the trade designation "CP-343-3 (25%)" or "CP-343-1 (25%)" in combination with toluene and sulfonated castor oil and sodium lauryl sulfate as surfactants. That composition, after it is formulated, is dispersed in de-ionized water to form an aqueous dispersion for use as a primer for polypropylene.
Both of these chlorinated polyolefins are marketed by Eastman as solvent solutions containing 25 percent by weight of the chlorinated polyolefin and 75 percent by weight of xylene as the solvent. Thus, for every 100 parts by weight of the aqueous dispersion, a full third of the composition is aromatic solvent which evaporates into the atmosphere in the use of the primer composition.
There has been a long standing environmental and ecological concern about the relatively high amounts of volatile organic solvents emitted to the atmosphere from the use of various liquid products. The Environmental Protection Agency or EPA requires that solvent emissions from a variety of product applications be reduced to the minimum possible amount. Maximum allowable limits are usually based on concepts known as Best Availability Control Technology or BACT and Reasonable Available Control Technology or RACT.
Product classes which include adhesion promoters or primers for polyolefins presently allow use of compositions having an extremely high solvent content because the EPA agrees that no better technology exists.
The EPA typically expresses the magnitude of solvent emissions for a given product application by a "volatile organic compounds" or VOC value. That VOC is usually expressed as the pounds of organic solvent per gallon of thinned product, excluding water, at the point of application. Thus, for a composition containing both water and organic solvent, the VOC computation, according to the EPA rule, requires that the combination of all ingredients with the exception of water be proportioned to one gallon. The total resulting pounds of organic solvents in that quantity of composition, therefore, reflects the VOC value.
By that definition, water must be excluded, and simply diluting a product with greater amounts of water does not decrease that product's VOC value.
The formulations suggested by Eastman for a non-aqueous primer have a VOC of approximately 6.9, while its suggested formulation for an aqueous primer has a VOC of about 6.2. Commercial products typically used today average about 6.9 VOC. VOC values of 6.2 and 6.9 are extremely high values. Because commercial formulations typically involve VOC values in excess of 6, there is a substantial need for an adhesion promoting composition which exhibits a VOC not substantially above 0.
Many such composition have been proposed. See, for example, U.S. Pat. Nos. 2,664,378, 3,398,046 and 4,981,730. Those compositions previously used in the treatment of polyolefin surfaces have contained high volatile organic solvent levels, and, therefore, high VOC values. Thus, there is a need for products having a VOC value of about 0.